Electrical apparatus



July 16, 1 946. SHORTY I 2,404,254

ELECTRICAL APPARATUS Filed Feb. 2, '1945 Inventor'- Thomas T Short,

Hi Attovney.

Patented July 16, 1946 ELECTRICAL APPARATUS Thomas Short, Fort Wayne,'Ind., assignor to General Electric Company, a corporation of New YorkApplication February 2, 1943, Serial No. 474,424

'3 Claims. 1

My invention relates to an electric apparatus suitable for operatingelectric discharge devices such as fluorescent lamps.

The operation of eleotric'discharge devices usually requires somesort-of a ballast, and it has been customary to employ'auto transformersfor stepping up the voltage when a sufiicient amount of voltage is notpresent and a reactor in series with theauto transformer and lamp foracting as a ballast. In the manufacturing of these ballasts it has beencustomary to employ separate core structures for the auto transformer,and each of the reactors, and then place these separate core structuresin a single casing,

An Object of my invention is to form an electrical apparatus foroperating a pair of lamps in which all the coils are mounted on anintegral core structure.

Another object of my invention is to balance suitably the flux flowingthrough the various legs of the core structure.

My invention will be more fully set forth in the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out in the claims annexed toand forming a part of this specification.

Referring to the drawing, in Fig. 1 a conventional lamp circuit is shownincluding an auto transformer Hl coil-connected across a suitable sourceof supply ll. One end of the auto transformer is grounded at 12 and theother end is connected to ballasting elements including reactor coils l3and It. The coil I3 is connected to a lamp i5, and the coil I4 isconnected to a lamp I 8. In order to have the lamps fire out of phase, acapacitor I! is connected between the coil l4 and the lamp 16.

In Fig. 2 I have illustrated my improved 5-legged' core suitable foroperating a pair of fluorescent lamps and include a core structure 20including legs A, B, C, D, and F. The coil [0 sur rounds the winding legC and is connected to the suitable source of supply and acts as an autotransformer. The coil which surrounds the leg A may be connected toeither the lead or the lag lamp, and in the construction illustrated inthe drawing, the winding leg A is surrounded by the coil l3 which isconnected to the lag lamp, while the leg F is surrounded by the coil Mwhich is connected to the lead lamp. In order to operate the devicesuccessfully, I have found that it is necessary that the sum of thefluxes through the legs A and F shall equal in magnitude the fiuxflowing through the center leg C. By doing this it is possible to reducethe cross sectional area of the legs B and D to 'a minimum, asthe'fiux'i'n the various legs A, C and F are out of phase,'and bybalancing the fluxes in this manner the legs B and D need only carrythe'vector difference 'of these fluxes.

Since the coil IE1 is connected to a separate source 'o'frsupply and thecoils l3 and 14 are connected to a load, we may consider that in thisapparatus there are three separate sources forcing flux through the corestructure, and in order to balance the fluxes in the manner describedabove it is necessary to choose the relationship between the number ofturns and the cross sectional area of the winding legs so that thearithmetic sum of the fluxes in the two outside legs will equal the fluxin the center leg. Given a certain value of flux in the center leg C,which, of course, is determined by the number of turns in the coil inand the voltage across which the coil ii! is connected, there will be acertain optimum value of relationship between the number of turns andthe area of the legs for the coils surrounding the two outside legs.This optimum of turns in coils l3 and i4 is such that the flux in thelegs A and F will add up to equal the total flux in the leg C. Assuminga uniform core density in the three legs, then the sum of the areas ofthe legs A and F shall equal the cross sectional area of leg C. If,however, the core densities are not equal, the cross sectional area willvary inversely with the differences in density.

Since the current flowing through the coils I3 and M are out-of-phase byabout degrees and each is about 30 degrees out-of-phase with the currentflowing through the main transformer winding ID, the fluxes passingthrough the legs A and F will be out-of-phase by about 60 degrees. Sincethe flux in the reactor legs A and F is outof-phase with the fluxpassing through the leg C by approximately 30 degrees, the two legs Band D must carry the unbalance or the vector difference between the fluxin the outside legs and the center leg.

Although I have shown and described particular embodiments of myinvention, I do not desire to be limited to the particular embodimentsdescribed, and I intend in the appended claims to cover allmodifications which do not depart from the spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric apparatus for operating lead and lag discharge lampsincluding a five legged core, an autotransformer coil around a centerleg and being adapted to be connected to a source of supply, a ballastreactor coil around one outside leg having one end adapted to beconnected to the lag lamp, another ballast reactor coil around anotheroutside leg having one end adapted to be connected to a lead lamp, theother ends of said ballast reactor coils being connected to saidtransformer, the size of the legs and the number and direction of turnsbeing so adjusted that the arithmetic sum of flux through the outsidelegs shall equal the flux in the center leg during normal operation, andwith the flux flowing through the fourth and fifth legs being the vectordiflerence between the flux in the center leg and in the outside legs.

2. In combination, a unitary five-legged core, a complete low leakagereactance transformer on one leg, separate reactor coils on two of theother legs respectively, said reactor coils being proportioned to carryequal currents which respectively lead and lag the transformer voltageby equal phase angles, the number of turns of said reactor coils beingequal to each other such that their respective fluxes are equal to halfthe transformer legs being less than the areas of the two lastmentionedcore legs and being adapted respectively to carry the vector resultantof half the transformer exciting flux and the flux of a different one ofsaid reactor coils, the relative polarities of said reactor coil fluxesbeing such that the fluxes in said two remaining legs are equal and ofminimum value which is substantially less than the flux in the reactorcoil carrying legs whereby the areas of said two remaining core legs areequal and can be a minimum which is substantially less than the area ofthe reactor coil carrying legs for equal flux density in all five corelegs.

3. An electric apparatus for operating a pair of electric dischargedevices comprising in combination, a magnetic core having five legs anda pair of yokes for respectively connecting the corresponding ends ofsaid legs, the center leg having an autotransformer winding mountedthereon, the two outside legs being each of half the crosssectional areaof the center leg, and a separate reactor winding on each of said outerlegs, the two remaining legs having equal cross-sectional areas whichare substantially less than the crosssectional area of the outer legs,the reactor coils being connected in parallel circuit relation with eachother and in series circuit relation with said transformer.

THOMAS T. SHORT.

